Counterintuitive DAC specs vs. sound

I don't have a stereophile system, nor money to acquire one, but I thought that I might perhaps spend just a bit more and make what improvements I'm able. Adding an affordable DAC sprang to mind; most of what I've read has said that doing this should help.

I am using a low-end, Toshiba HD DVD player to play music CD's. The player's spec sheet puts its internal DAC's at 24/192. I figured that'd be better than what my 'pre-amp' (Yamaha DSP-A1 a/v receiver) is likely to have, being 7 or 8 years old. (I emailed Yamaha to ask them for information about the DSP-A1's DACs's. I know from the manual that it is a '24 bit' resolution converter, but it doesn't say what the sampling frequency is. They never responded.) So, guessing that the DVD's newer, better spec'd DAC's were probably going to sound superior, for a long time I just used the player's analog outs.

Moreover, I reasoned, with a 24/192 internal DAC, why in the world would I want to add an external DAC (MSB's link DAC III is sort of in my price range), with "lesser" specs (the link DAC is a 24/96 converter)? So, I forgot about the whole thing, thinking it could make my system sound worse, not better.

One day on a whim, however, I decided to hook up the DVD player's optical out, and use the pre-amp's DACs instead of the DVD player's. Lo and behold, it sounds *much* better this way, even though each units' specifications tell me it should really be the other way around.

I do not understand this. And, if *this* counterintuitive situation is manifest, then maybe adding that external DAC might actually help, even though that'd be sort of counterintuitive too.